The present invention relates in general to heterogeneous charged, internal combustion engines, and, more in particular, to such an engine and process for its operation wherein one or more desired fluids have a tailored distribution in a combustion chamber achieved by forming clouds of the fluids at selected locations in an inlet channel during the quiet period between openings of the channel into the combustion chamber and inducting the clouds and air into the chamber by standard induction processes.
The problem of exhaust gas emission from internal combustion engines has become so serious that drastic legislation requires the reduction in the emissions of the oxides of nitrogen, unburned hydrocarbons, and carbon monoxide to extremely low levels relative to those produced by an engine without emission controls.
To achieve low emissions, internal combustion engines have been modified and are proposed to be modified in a number of ways. Modifications for emissions control include: making the fuel-to-air ratio leaner in fuel, exhaust gas recirculation into the combustion chamber, retardation of spark, and catalysis of exhaust gases to form harmless products. The controls have resulted in performance compromises in fuel economy, power and responsiveness.
Past experience has shown that it is difficult to make internal combustion engines run well when the mixture ratio of fuel and air is less than the stoichiometric ratio, that is, fuel-lean. In fact, the great majority of pre-emission controlled engines operated with mixture ratios rich in fuel. Because of the absence of sufficient air to burn the fuel completely, the exhaust of such engines contained relatively large amounts of unburned fuel and of carbon monoxide. If it were possible to operate internal combustion engines successfully at mixture ratios lean in fuel, the resulting exhaust would contain very little unburned fuel and very little carbon monoxide.
Oxides of nitrogen are produced in large quantities when combustion temperatures are high. Upon expansion and exhaust, the resultant cooling quenches the reactions and freezes the formed oxides, preventing a reversal of the reactions which formed the oxides. A reason for the relatively large quantity of nitric oxide emissions, it is thought, is that the first quantity of a homogeneous combustible mixture burned is compressed and elevated in temperature by the subsequent burning of the remainder of the charge, thereby enhancing the formation of oxides of nitrogen. Maximum combustion temperatures occur when mixture ratios are near stoichiometric and are at a maximum at slightly fuel-lean operation. When combustion temperatures are reduced, by using either rich or lean mixtures, or by introducing diluents such as water or recirculated exhaust gases, the production of oxides of nitrogen drops relatively rapidly.
Although in the past an important goal of internal combustion engine design has been the achievement of homogeneous mixtures of fuel and air in the combustion chamber at the time of ignition, it is now recognized that a careful tailoring of the distribution of fuel, air and diluents within the combustion chamber at the time of ignition can reduce emissions.
This recognition has led to the so-called stratified or heterogeneous charge engine as an attractive possibility for reducing noxious emissions. In such an engine, the overall temperature of combustion can be made relatively low because, among other things, the compression of the initially burned charge by subsequent combustion is not as great.
Briefly, a heterogeneous charge engine contemplates a tailored distribution of fuel and air. A portion of the charge is fuel-rich with enough air to support combustion. Typically, the remainder of the charge is a zone of either air, or a fuel-lean mixture of fuel and air. The fuel-rich charge is burned and supplies the energy necessary for the burning of any fuel in the lean zone. The effect of the tailored distribution in the engine is to reduce the overall average temperature of combustion. This results in reducing the formation of the oxides of nitrogen. A heterogeneous charge engine also allows combustion at considerably fuel-leaner average overall fuel-to-air ratios than is possible with a homogeneous charge. This lean operation also reduces carbon monoxide and unburned hydrocarbon emissions.
A form of heterogeneous charge engine contemplates the use of only one combustion chamber. Here a charge is stratified by directing two separate streams with different fuel-air ratios into different parts of the combustion chamber. An example of this approach is described in U.S. Pat. No. 3,364,911 to Baudry et al. Another single combustion chamber, stratified charge engine has been developed by the Texas Company and the Ford Motor Company. Their approach creates a swirl of air in the combustion chamber about the axis of the chamber. Fuel is injected into the swirl and a resulting fuel-rich charge is positively ignited by a spark plug.
Another heterogeneous charge engine employs an auxiliary chamber for the initial burning of the fuel-rich mixture. This chamber confines the mixture in the zone of the spark plug to ensure its presence there at the initiation of combustion. Fuel and air are admitted to the pre-chamber by an inlet valve. A separate inlet valve admits a lean mixture of fuel and air or just air into a second and larger chamber in communication with the auxiliary chamber. Combustion in the auxiliary chamber produces a flame front which spreads into the larger, main chamber for completion of combustion with air there and to supply the energy required to sustain combustion of fuel there.